FIG. 1 is a structural diagram of a protocol layer of a broadband wireless access system. A broadband wireless access system defines a protocol of a medium access control (hereinafter abbreviated ‘MAC’) and a physical (hereinafter abbreviated ‘PHY’) layer for a point-to-multipoint connection between a base station and a mobile terminal. In the present specification, a mobile terminal includes a mobile subscriber station (MSS) capable of performing a handover between at least one or more base stations and a subscriber station (SS) capable of wireless communications within one access point (AP) or a base station.
A highest port of a MAC layer, which is a service specific convergence sublayer, transforms packet data of various upper core networks into a common protocol data unit (hereinafter abbreviated PDU) according to MAC specifications and compresses a header of a corresponding packet.
FIG. 2 is a flowchart of an initialization procedure of a mobile terminal in a broadband wireless access system. Referring to FIG. 2, if a power of a mobile terminal is turned on, the mobile terminal searches a downlink channel, acquires uplink/downlink synchronization with a base station and receives a downlink MAP (DL-MAP) message, an uplink MAP (UL-MAP) message, a downlink channel descriptor (hereinafter abbreviated ‘DCD’) message and an uplink channel descriptor (hereinafter abbreviated ‘UCD’) message from a base station to acquire uplink/downlink channel parameter (S21).
The mobile terminal adjusts an uplink transport parameter by performing ranging with the base station and a basic management CID and a primary management CID are allocated to the mobile terminal by the base station (S22). And, the mobile terminal performs a negotiation with the base station for base station (S23). Moreover, authentication for the mobile terminal is carried out (S24). And, a secondary management CID is allocated by the base station to the mobile terminal managed with IP through a registration to the base station (S25). An IP connection is configured (S26). A current date and time are set (S27). And, a connection for a previously prepared service is configured by downloading a configuration file of the mobile terminal from a TFTP server (S29).
In the course of performing the initial network registration process, as shown in FIG. 2, a procedure that the mobile terminal adjusts transport parameters (frequency offset, time offset, transmit power) for an uplink communication with the base station is called a ranging. After completion of the network registration process, the mobile terminal periodically performs the ranging to keep maintaining the uplink communication with the base station continuously.
A physical layer of a broadband wireless access system transmits a signal according to a single carrier or multi-carrier system. As an example of the multi-carrier system, orthogonal frequency division multiplexing (hereinafter abbreviated ‘OFDM) can be used. Meanwhile, as an access system for allocating a resource by a subchannel unit generated from grouping portions of carriers, orthogonal frequency division multiple access (hereinafter abbreviated ‘OFDMA’) can be used.
FIG. 3 is a diagram of a subchannel of an OFDMA physical layer. In the example shown in FIG. 3, there are three subchannels each of which is constructed with two subcarriers. In this case, carriers configuring the subchannels may exist adjacent to each other or can be equally spaced apart from each other. Thus, in case that a multiple access is enabled by the subchannel unit, frequency diversity gain, gain according to power concentration and forward power control can be efficiently performed.
FIG. 4 is a diagram of an example of a data region for defining OFDMA resource allocation. Referring to FIG. 4, a slot allocated to each mobile terminal is defined by a data region of a 2-dimensional space, which is a set of continuous subchannels assigned by a burst. Namely, one data region in OFDMA, as shown in FIG. 4, can be represented as a rectangle determined by a time coordinate and a subchannel coordinate.
The data region can be allocated to an uplink transmission of a specific mobile terminal. And, in downlink, data can be transmitted to a mobile terminal via specific-data region. In order to define the data region on 2-dimension, the number of OFDM symbols in a time domain and the number of continuous subchannels starting from a position distant from a reference point by an offset in a frequency domain should be allocated.
FIG. 5 is a diagram of a mapping method between subchannel/OFDM symbol of FEC. MAC data is segmented according to a size of forward error correction (hereinafter abbreviated ‘FEC’) block. And, each FEC block is extended to occupy three OFDM symbols on a time axis of each subchannel. If an end of a data region is reached by performing mapping on each FEC block continuously in a manner of incrementing a subchannel number, the mapping keeps being performed from an OFDM symbol having a subsequent lower number in the same manner.
FIG. 6 is a structural diagram of an OFDM physical layer frame of time division duplexing (hereinafter abbreviated ‘TDD’). Referring to FIG. 6, a downlink subframe starts from a preamble used for synchronization and equalization in a physical layer. A downlink MAP (DL-MAP) message and an uplink MAP (UL-MAP) message in a broadcast format defining positions and usages of bursts allocated to an uplink and a downlink, respectively follow the preamble in sequence to define an overall structure of a frame.
Table 1 shows an example of a downlink MAP (DL-MAP) message.
TABLE 1SyntaxSizeNotesDL-MAP_Message_Format( ){ Management   Message8 bitsType = 2 PHY  SynchronizationvariableSee appropriate PHYFieldspecification DCD Count8 bits Base Station ID48 bits  Begin  PHY  SpecificSee applicable PHY section.Section {  for(i=  1;  i  <=For each DL-MAP element 1n;i++)  {to n.  DL-MAP_IE( )variableSee corresponding PHYspecification.  } if  !(byte boundary){  Padding Nibble4 bitsPadding to reach byteboundary.  } }} if  !(byte boundary){  Padding Nibble4 bitsPadding to reach byteboundary.  } }
Table 2 shows an example of an uplink MAP (UL-MAP) message.
TABLE 2SyntaxSizeNotesUL-MAP_Message_Format( ){ Management   Message8 bitsType = 3 Uplink Channel ID8 bits UCD Count8 bits Allocation Start Time32 bits   Begin  PHY  SpecificSee applicable PHY section.Section {   for(i=  1;  i  <=  n;For each UL-MAP element 1i++)  {to n.   UL-MAP_IE( )variableSee corresponding PHYspecification.  }  } if !(byte boundary) {  Padding Nibble4 bitsPadding to reach byteboundary. }}
A downlink MAP (DL-MAP) message defines a usage allocated per burst for a downlink region in a burst mode physical layer. Meanwhile, an uplink MAP (UL-MAP) message defines a usage allocated per burst for an uplink region.
A usage of an information element configuring a UL-MAP message is decided by an uplink interval usage code (UIUC) per CID and a position of a corresponding region can be regulated by a ‘duration’ field. A per region usage is decided according to a UIUC value used by the UL-MAP. And, each region starts from a point distant from a previous IE start point by a duration regulated by UL-MAP IE.
Table 3 shows an example of DL-MAP IE.
TABLE 3SyntaxSizeNotesDL-MAP_IE( ) { DIUC4 bits if (DIUC  == 15){ Extended  DIUCvariabledependent IE } else { if  (INC_CID ==The DL-MAP starts with INC_CID =1)  {0. INC_CID is toggled between 0and 1 by the CID-SWITCH_IE( ) N_CID8 bitsNumber of CIDs assigned for thisIE for  (n=0;  n<N_CID; n++) {  CID16 bits   } } OFDMA  Symbol8 bitsoffset Subchannel6 bitsoffset Boosting3 bits000: normal (not boosted)001: +6 dB010: −6 dB011: +9 dB100: +3 dB101: −3 dB110: −9 dB111: −12 dB No.   OFDMA7 bitsSymbols No.6 bitsSubchannels Repetition2 bits0b00 - No repetition codingCoding0b01 - Repetition coding of 2Indicationused0b10 - Repetition coding of 4used0b11 - Repetition coding of 6used  } }
As shown in the example of Table 3, an information element (hereinafter abbreviated ‘IE’) configuring a downlink MAP (DL-MAP) discriminates a downlink traffic region corresponding to each mobile terminal through such position information of burst as a downlink interval usage code (DIUC), a connection ID, a subchannel offset, a symbol offset, a number of subchannels and a number of symbols.
Table 4 shows an example of UL-MAP IE.
TABLE 4SyntaxSizeNotesUL-MAP_IE( ) { CID16 bits  UIUC4 bits if(UIUC==12){ OFDMA Symbol offset8 bits Subchannel offset7 bits No. OFDMA Symbols7 bits No. Subchannels7 bitsRanging Method2 bits0b00 - InitialRanging/Handover Rangingover two symbols0b01 - InitialRanging/Handover Rangingover four symbols0b10 - BW request/PeriodicRanging over one symbol0b11 - BW request/PeriodicRanging over three symbols }  else  if  (UIUC  ==14)  { CDMA_Allocation_IE( )32 bits  Else if (UIUC==15){ Extended     UIUCvariabledependent IE }else{ Duration10 bits In OFDMA slots Repetition   coding2 bitsindication } Padding  nibble,  if4 bitsCompleting to nearest byte,neededshall be set to 0. }}
An uplink region defined by UIUC 12 is allocated for a usage for an initial ranging, handover ranging, periodic ranging or bandwidth request and, is allocated on the basis of contention.
In an OFDMA system applied to a broadband wireless access system, a mobile terminal performs a ranging request and an uplink bandwidth request for adjusting an uplink transmission parameter using CDMS code. Namely, a base station broadcasts to transmit a CDMA code set for the ranging and uplink bandwidth requests to mobile terminals via an uplink channel descriptor (UCD). And, the mobile terminal randomly selects a ranging code suitable for a usage from the received CDMA code set and then transmits it in an uplink region allocated for a ranging.
Table 5 shows an example of UCD message.
TABLE 5SyntaxSizeNotesUCD_Message_Format( ){ Management Message Type = 08 bits Configuration Change Count8 bits Ranging Backoff Start8 bits Ranging Backoff End8 bits Request Backoff Start8 bits Request Backoff End8 bits TLV  Encoded  information  forVariableTLV specificthe overall channel Begin PHY Specific Section{ for(i=0; i<=n; i++){For each uplinkburst profile 1 to n Uplink_Burst_ProfileVariablePHY specific } }}
Table 6 shows examples of ranging and bandwidth request associated TLV parameters included in UCD message.
TABLE 6TypeName(1 byte)LengthValueInitial ranging1501Number of initial rangingcodesCDMA codes. Possible valuesare 0-255.aPeriodic ranging1511Number of periodic rangingcodesCDMA codes. Possible valuesare 0-255.aHandover ranging1Number of handover rangingcodesCDMA codes. Possible valuesare 0-255.aBandwidth request1521Number of bandwidth requestcodescodes. Possible values are0-255.aPeriodic ranging1531Initial backoff window sizebackoff startfor periodic rangingcontention, expressed as apower of 2. Range: 0-15(the highest order bitsshall be unused and set to0).Periodic ranging1541Final backoff window sizebackoff endfor periodic rangingcontention, expressed as apower of 2. Range: 0-15(the highest order bitsshall be unused and set to0).Start of ranging1551Indicates the startingcodes groupnumber, S, of the group ofcodes used for this uplink.All the ranging codes usedon this uplink will bebetween S and((S + N + M + L + O)mod 256). Where, N is thenumber of initial-rangingcodes. M is the number ofperiodic-ranging codes. Lis the number of bandwidth-request codes. O is thenumber of initial-rangingcodes. M is the number ofhandover-ranging codes. Therange of values is 0S ≦≦ 255
A downlink channel descriptor (DCD) message and an uplink channel descriptor (UCD) message are MAC management messages including uplink and downlink channels parameters of a base station, respectively. The base station periodically transmits the downlink channel descriptor (DCD) message and the uplink channel descriptor (UCD) message to mobile terminals within an area.
Each of the terminals obtains information for coding and modulation schemes corresponding to the respective bursts via the DCD/UCD message and then codes/decodes data using the obtained information. The mobile terminal decides whether a channel parameter of the base station is changed and then updates the channel parameter. Meanwhile, the UCD message includes the CDMZ code set associated with the ranging and bandwidth requests and information for a backoff time applied to a code collision after the code transmission.
The base station allocates ranging regions to the mobile terminals on the basis of contention via an uplink map information element. In this case, according to a usage of ranging, the ranging regions can be allocated by being divided into an initial ranging and handover ranging region and a periodic ranging and bandwidth request region. In the following description, the initial ranging and handover ranging region and the periodic ranging and bandwidth request region are abbreviated ‘ranging and bandwidth request region’.
The base station having received the ranging code sets to deliver a transmission power adjustment value, a time and frequency adjustment value, a ranging status (success, fail) and the like necessary for uplink synchronization of the mobile terminal via a ranging response (RNG-RSP) message.
Table 7 shows an example of a ranging response message.
TABLE 7SyntaxSizeNotesRNG-RSP_Message_Format( ){ Management   Message8 bitsType = 5 Uplink Channel ID8 bits TLV      EncodedvariableTLV specificInformation }
Table 8 shows an example of TLV parameter included in a ranging message.
TABLE 8TypeName(1 byte)LengthValue (variable-length)Timing14Tx timing offset adjustmentAdjust(signed 32-bit). The timerequired to advance SStransmission so frames arrive atthe expected time instance atthe BS. Units are PHY specific(see 10.3)Power Level21Tx Power offset adjustmentAdjust(signed 8-bit, o.25 Db units)specifies the relative change intransmission power level thatthe SS is to make in order thattransmission arrive at the BS atthe desired power.When subchannelization isemployed, the subscriber shallinterpret the power offsetadjustment as a required changeto the transmitted powerdensity.Offset34Tx frequency offset adjustmentFrequency(signed 32-bit, Hz units)Adjustspecifies the relative change intransmission frequency that theSS is to make in order to bettermatch the BS. (This is fine-frequency adjustment within achannel, not reassignment to adifferent channel.)Ranging41Used to indicate whether uplinkStatusmessages are received withinacceptable limits by BS.1 = continue,2 = abort,3 = success,4 = rerangeRanging1504Bits 31 to 22: Used to indicatecodethe OFDM time symbol referenceattributesthat was used to transmit theranging codeBits 21 to 16: Used to indicatethe OFDMA subchannel symbolreference that was used totransmit the ranging codeBits 15 to 8: Used to indicatethe ranging code index that wassent by the SSBits 7 to 0: The 8 leastsignificant bits of the framenumber of the OFDMA frame wherethe SS sent the ranging code
In case that the base station allocates an uplink bandwidth, in order for the mobile terminal to perform the ranging or bandwidth request, UIUC is set to 12 and a ranging method suitable for each usage is set up. And, an uplink MAP message including such an uplink MPA IE as the example shown in Table 4.
The initial ranging and handover ranging region and the bandwidth request and periodic ranging region can be allocated each frame on the basis of contention. In this case, an uplink MAP IE for the ranging or bandwidth request region allocation per frame should be included in the uplink MAP message. Yet, if the ranging and bandwidth request region is not frequently changed, ranging and bandwidth request region allocation information is included in an uplink channel descriptor message periodically transmitted by the base station instead of including the uplink MAP IE for the ranging and bandwidth request region allocation in the uplink MAP message each frame. In this case, by reducing a size of the uplink MAP message, the base station can prevent the waste of radio resources and the mobile terminal can reduce power for decoding the uplink MAP message.
Table 9 shows an example of downlink prefix (DL Frame Prefix).
TABLE 9SyntaxSizeNotesDL_Frame_Prefix_Format( ) {Used subchannel bitmap6 bitsBit #0: Subchannels 0-11are usedBit #1: Subchannels 12-19are usedBit #2: Subchannels 20-31are usedBit #3: Subchannels 32-39are usedBit #4: Subchannels 40-51are usedBit #5: Subchannels 52-59are usedRanging_Change_Indication1 bitRepetition_Coding_Indication2 bits00: No repetitioncoding on DL-MAP01: Repetition codingof 2 used on DL-MAP02: Repetition codingof 4 used on DL-MAP11: Repetition codingof 6 used on DL-MAPCoding_Indication3 bits0b000: CC encoding usedon DL-MAP0b001: BTC encodingused on DL-MAP0b010: CTC encodingused on DL-MAP0b011: ZT CC used onDL-MAP0b100 to 0b111:ReservedDL-MAP_Length8 bitsreserved4 bitsShall be set to zero}
A downlink prefix is placed ahead of a DL-MAP message (‘FCH’ in FIG. 6) and includes information associated with a current frame.
In the downlink prefix shown in Table 9, ‘Ranging Change Indication’ parameter is a flag that indicates whether an uplink ranging and bandwidth request region of a current frame is changed by being compared to that of a previous frame. For instance, if it is changed, the ‘Ranging Change Indication’ parameter is set to ‘1’. If not, the ‘Ranging Change Indication’ parameter can be set to ‘0’. In this case, in a frame having ‘Ranging Change Indication’ field set to ‘0’. It can be indicated that a ranging and bandwidth request region of an uplink is identical to that of a previous frame. And, an uplink MPA information element associated with allocation information of the ranging and bandwidth request region can be omitted.
A MAP information element associated with an allocation of a ranging and bandwidth request region can be omitted from an uplink MAP message or included therein each frame. Namely, a base station compares a current frame to a previous frame. If a ranging and bandwidth request region of the current frame is not changed, a ranging region change indication field of the downlink frame prefix shown in Table 9 is set to represent that the ranging region of the current frame is not changed from that of the previous frame. And, the MAP information element associated with the ranging and bandwidth request region can be omitted.
However, in this case, in order for a mobile terminal, which firstly make a registration to a network or performs a handover, to perform an initial ranging or to make a bandwidth request, the mobile terminal should wait until receiving an uplink MAP including a MAP information element associated with a ranging and bandwidth request region allocation from a base station. Moreover, in case that a base station has to transmit an uplink MAP message by including a MAP information element associated with a ranging and bandwidth request region allocation in the message each frame, the base station wastes its resources and power is consumed for a mobile terminal to decode the MAP information element associated with the ranging and bandwidth request region allocation each time.